Measurement of ocular tumor volumes from serial, cross-sectional ultrasound scans.

A system has been developed to determine intraocular tumor volume, a characteristic that has been estimated in previous studies from linear dimensions using a variety of models. Volume was determined by tracing tumor boundaries in sequential, parallel ultrasound scans, adding the areas and multiplying by the interslice interval. The in vitro accuracy of the technique was within +/- 2%. The mean difference between volumes determined from replicate in vivo scans of intraocular tumors was 4.3%. Serial scan volumes were, on average, 19% smaller than volumes computed from an ellipsoidal model and 13% smaller than area-rotational volumes. Differences of as much as 50% were observed between serial scan volumes and volumes computed with these models. The results indicate that methods based on either linear measurements or the tumor area in a single cross-section will tend to both systematically overestimate tumor volume and suffer from unpredictable, nonsystematic errors.